Tools for the accurate measurement of flow in a sewer network are an important resource for managers, mechanics, engineers, and regulators of municipal and industrial sewer networks. Accurate measurements of flow between points, and an understanding of what flow is expected to occur at a downstream point based on upstream conditions, can help determine—and to predict—when network problems such as leaks, breaks, clogs and other blockages and overflows may occur. They can also help system engineers and designers understand when additional capacity must be built into the system, as well as to help them better manage a network with its existing capacity.
One key parameter that is measured in a sewer network is the net flow between two or more points. At a basic level, the volume of flow at a downstream location minus the volume of flow at an upstream location is considered to be the net flow between the two locations. The downstream location volume is typically higher than that of the upstream location under normal conditions, as discharge sources, rainwater inflow and infiltration, and/or other sources may introduce wastewater into the network between the upstream and downstream locations. If the net flow between the two locations decreases below what is expected, or if net flow becomes negative, the network manager should investigate to determine whether a leak, break, clog, or overflow is occurring.
However, the above-described general calculation of net flow does not consider that it takes time for a particular flow element to travel from the upstream location to the downstream location, nor does it consider that such time may vary. Thus, because of the “travel time,” by the time that a flow reaches a downstream location from an upstream location, the conditions at the upstream location may have become significantly different due to changes in input volumes, changes in weather conditions, or any number of conditions. Thus, the traditional way of calculating net flow is not desirable because it does not account for travel time or variations in travel time.
Sewer network managers have tried to compensate for the above-described problem in two ways. The first way is to use a larger number of monitoring points in the network, so that conditions are not likely to significantly change during the time that it takes wastewater to flow from one monitor to the next. However, flow monitors can be very expensive to purchase and costly to maintain. Thus, this solution is not desirable because it is not cost-effective, and it is often cost-prohibitive. In addition, the solution still does not account for the travel time between the monitors that are installed.
The second way is to perform detailed modeling of travel time, based on volumes of network design specifications and flow data. Such modeling exercises are time-consuming, costly, and only provide a snapshot of an anticipated travel time that matches the conditions under which the modeling occurred.
Thus, if a method and system for determining travel time in a sewer network were available that could determine the travel time in real time, using a small number of monitors and relatively little input data, significant cost savings would result, and sewer network managers would be better able to manage, predict conditions, anticipate design requirements, and respond to problems in their networks.
Accordingly, it is desirable to provide an improved method and system for analyzing flow in a sewer network that includes the real-time derivation of the time that it takes for a flow to travel between points in the network.